During that time, his Intel team had six silicon photonics papers published in the science journals, Nature and Nature Photonics, and held several world records - for the fastest modulator, first at 1 gigabit, then 10 gigabit and finally 40 gigabit, the first pulsed and continuous-wave Raman silicon laser, the first hybrid silicon laser working with The University of California, Santa Barbara, and the fastest silicon germanium photo-detector operating at 40 gigabit.It got to the stage where Intel’s press relations department would come and ask what the team would be announcing in the coming months. “ 'Hey guys,' I said, 'it doesn't work that way ' ”.
Since leaving Intel last year, Paniccia has been working as a consultant and strategic advisor. He is now exploring opportunities for silicon photonics but in segments other than telecom and datacom.
“I didn't want to go into developing transceivers for other big companies and compete with my team's decade-plus of development; I spent 20 years at Intel,” he says.
Decade of development
Intel’s silicon photonics work originated in the testing of its microprocessors using a technique known as laser voltage probing. Infra-red light is applied to the back side of the silicon to make real-time measurements of the chip’s switching transistors.
For Paniccia, it raised the question: if it is possible to read transistor switching using light, can communications between silicon devices also be done optically? And can it be done in parallel to the silicon rather than using the back side of silicon?
In early 2000 Intel started working with academic Graham Reed, then at the University of Surrey, and described by Paniccia as one of the world leaders in silicon photonics devices. “We started with simple waveguides and it just progressed from there,” he says.
The Intel team set the target of developing a silicon modulator working at 1 gigahertz (GHz); at the time, the fastest silicon modulator operated at 10 megahertz. “Sometimes leadership is about pushing things out and putting a stake in the ground,” he says.
It was Intel’s achievement of a working 1GHz silicon modulator that led to the first paper in Nature. And by the time the paper was published, Intel had the modulator working at 2GHz. The work then progressed to developing a 10 gigabit-per-second (Gbps) modulator and then broadened to include developing other silicon photonics building-block devices that would be needed alongside the modulator – the hybrid silicon laser, the photo-detector and other passive devices needed for an integrated transmitter.
There is a difference between proving the technology works and making a business out of it
Once 10Gbps was achieved, the next milestone was 20Gbps and then 40Gbps. Once the building block devices achieved operation in excess of 40Gbps, Intel’s work turned to using these optical building blocks in integrated designs. This was the focus of the work between 2010 to 2012. Intel chose to develop a four-channel 40Gbps (4x10 gigabit) transceiver using four-wavelength coarse WDM which ended up working at 50Gbps (4x12.5 gigabit) and then, most recently, a 100Gbps transceiver.
He says the same Intel team is no longer talking about 50Gbps or 100Gbps but how to get multiple terabits coming out of a chip.
Status
Paniccia points out that in little more than a decade, the industry has gone from not knowing whether silicon could be used to make basic optical functions such as modulators and photo-detectors, to getting them to work at speeds in excess of 40Gbps. “I’d argue that today the performance is close to what you can get in III-V [compound semiconductors],” he says.
He believes silicon photonics is the technology of the future, it is just a question of when and where it is going to be applied: “There is a difference between proving the technology works and making a business out of it”.
In his mind, these are the challenges facing the industry: proving silicon photonics can be a viable commercial technology and determining the right places to apply it.
For Paniccia, the 100-gigabit market is a key market for silicon photonics. “I do think that 100 gigabit is where the intercept starts, and then silicon photonics becomes more prevalent as you go to 200 gigabit, 400 gigabit and 1 terabit,” he says.
So has silicon photonics achieved its tipping point?
Paniccia defines the tipping point for silicon photonics as when people start believing the technology is viable and are willing to invest. He cites the American Institute for Manufacturing Integrated Photonics (AIM Photonics) venture, the $610 million public and private funded initiative set up in 2015 to advance silicon photonics-based manufacturing. Other examples include the silicon photonics prototyping service coordinated by nano-electronics research institute imec in Belgium, and global chip-maker STMicroelectronics becoming a silicon photonics player having developed a 12-inch wafer manufacturing line.
Instead of one autonomous LIDAR system in a car, you could have 20 or 50 or 100 sprinkled throughout your vehicle
“All these are places where people not only see silicon photonics as viable but are investing significant funds to commercialise the technology,” says Paniccia. “There are numerous companies now selling commercialised silicon photonics, so I think the tipping point has passed.”
Another indicator that the tipping point has happened, he argues, is that people are not spending their effort and their money solely on developing the technology but are using CMOS processes to develop integrated products.
“Now people can say, I can take this process and build integrated devices,” he says. “And when I put it next to a DSP, or an FPGA, or control electronics or a switching chip, I can do things that you couldn't do next to bulky electronics or bulky photonics.”
It is this combination of silicon photonics with electronics that promises greater computing power, performance and lower power consumption, he says, a view shared by another silicon photonics luminary, Rockley Photonics CEO, Andrew Rickman.
Moreover, the opportunities for integrated photonics are not confined to telecom and datacom. “Optical testing systems for spectroscopy today is a big table of stuff - lasers, detectors modulators and filters,” says Paniccia. Now all these functions can be integrated on a chip for such applications as gas sensing, and the integrated photonics device can then be coupled with a wireless chip for Internet of Things applications.
The story is similar with autonomous vehicle systems that use light detection and ranging (LIDAR) technology. “These systems are huge, complicated, have a high power consumption, and have lots of lasers that are spinning around,” he says. “Now you can integrate that on a chip with no moving parts, and instead of one autonomous LIDAR system in a car, you could have 20 or 50 or 100 sprinkled throughout your vehicle”
Disruptive technology
Paniccia is uncomfortable referring to silicon photonics as a disruptive technology. He believes disruption is a term that is used too often.
Silicon photonics is a technology that opens up a lot of new possibilities, he says, as well as a new cost structure and the ability to produce components in large volume. But it doesn’t solve every problem.
The focus of the optical vendors is very much on cost. For markets such as the large-scale data centre, it is all about achieving the required performance at the right cost for the right application. Packaging and testing still account for a significant part of the device's overall cost and that cannot be forgotten, he says.
Paniccia thus expects silicon photonics to co-exist with the established technologies of indium phosphide and VCSELs in the near term.
“It is all about practical decisions based on price, performance and good-enough solutions,” he says, adding that silicon photonics has the opportunity to be the mass market solution and change the way one thinks about where photonics can be applied.
“Remember we are just at the beginning and it will be very exciting to see what the future holds.”